bug#7225: 23.2.50; [PATCH] C-c C-c doesn't work in shell mode (Cygwin)

[Ken Brown]

On 10/16/2010 3:32 AM, Eli Zaretskii wrote:
> > Date: Fri, 15 Oct 2010 19:36:36 -0400
> > From: Ken Brown<kbrown@cornell.edu>
> > Cc:
> >
> > I think I can fix a longstanding bug in the Cygwin build of emacs, in
> > which C-c C-c doesn't work to interrupt a process in shell mode.  Since
> > the problem doesn't seem to be in the bug database, I'm reporting it
> > first for documentation purposes, and then I'll give the proposed fix.
> > To reproduce:
> >
> > emacs -Q
> > M-x shell
> > cat
> > C-c C-c
> > (The cat process doesn't get killed.)
>
> Is the reason for this known?  It looks like the `kill' syscall isn't
> doing its job, but if that's so, there should be a good reason for
> that.

The problem is the group id in the call to 'kill'.  Cygwin doesn't 
define TIOCGPGRP, and the group id as set in line 6233 of process.c 
(emacs-23 branch) is the wrong group id.

> > The following patch seems to fix it:
> >
> > === modified file 'src/s/cygwin.h'
> > --- src/s/cygwin.h      2010-01-13 08:35:10 +0000
> > +++ src/s/cygwin.h      2010-10-15 22:20:39 +0000
> > @@ -132,6 +132,9 @@
> >       returns ENOSYS.  A workaround is to set G_SLICE=always-malloc. */
> >    #define G_SLICE_ALWAYS_MALLOC
> >
> > +/* Send signals to subprocesses by "typing" special chars at them.  */
> > +#define SIGNALS_VIA_CHARACTERS
> > +
> >    /* the end */
> >
> >    /* arch-tag: 5ae7ba00-83b0-4ab3-806a-3e845779191b
> >
> > I'd like to apply this to the emacs-23 branch.  Does anyone see a
> > problem with it or anything further I should test?
>
> Did you test it with a subprogram that puts its stdin into a mode
> where (speaking in termios terms) the ISIG flag in c_lflag passed to
> tcsetattr is unset?

I don't know how to do this.  Can you give me a short test program to try?

> In any case, I wouldn't recommend to take this workaround unless we
> understand why this doesn't work without it.

I'm not sure why you call it a workaround.  The comments preceding (and 
in) the definition of process_send_signal make it clear that 
SIGNALS_VIA_CHARACTERS is the preferred method.  It's used by GNU/Linux 
(see src/s/gnu-linux.h) and several other systems.